diff --git a/lib/std/io/io.c3 b/lib/std/io/io.c3
index 570fd1463..41ca32604 100644
--- a/lib/std/io/io.c3
+++ b/lib/std/io/io.c3
@@ -57,6 +57,11 @@ faultdef
  @return `The string containing the data read.`
 *>
 macro String? readline(Allocator allocator, stream = io::stdin())
+{
+	return readline_impl{$typeof(stream)}(allocator, stream);
+}
+
+fn String? readline_impl(Allocator allocator, Stream stream) <Stream> @private
 {
 	if (allocator == tmem)
 	{
@@ -99,16 +104,21 @@ macro String? treadline(stream = io::stdin())
 *>
 macro usz? readline_to_stream(out_stream, in_stream = io::stdin())
 {
-	bool $is_stream = $typeof(in_stream) == InStream;
+	return readline_to_stream_impl{$typeof(in_stream), $typeof(out_stream)}(out_stream, in_stream);
+}
+
+fn usz? readline_to_stream_impl(OStream out_stream, IStream in_stream) <IStream, OStream> @private
+{
+	bool $is_stream = IStream == InStream;
 	$if $is_stream:
-		var func = &in_stream.read_byte;
+		var func @safeinfer = &in_stream.read_byte;
 		char val = func((void*)in_stream)!;
 	$else
 		char val = in_stream.read_byte()!;
 	$endif
-	bool $is_out_stream = $typeof(out_stream) == OutStream;
+	bool $is_out_stream = OStream == OutStream;
 	$if $is_out_stream:
-		var out_func = &out_stream.write_byte;
+		var out_func @safeinfer = &out_stream.write_byte;
 	$endif
 
 	if (val == '\n') return 0;